MEMS vacuum packaging, the technology for providing gas-tightness enclosure with an internal tiny cavity, has been a key technology for various MEMS devices and systems. Vacuum packaging protects micro devices and systems from external environments and allows easy handling. The stability of pressure is very important to ensure the dynamic performance of MEMS devices. Wafer level MEMS packaging is recently gaining momentum since it provides a practical pathway for cost reduction as the yield and volume increase. Keeping the vacuum environment in MEMS wafer level packages is really a technical challenge because of the high volume to surface ratio.
Pressure level is a key parameter for the quality of the MEMS devices. The pressure deterioration within a micro cavity is strongly related to the leakage of the packaging structure and the outgassing phenomena. Ultra-high vacuum conditions, such as 10 mTorr or less, for the MEMS packaging can be achieved using the getter technology. This technology utilizes the unique property of getter materials to sorb the residual gases trapped in the device during the manufacturing process and maintains the pressure at a very low level for the required lifetime by limiting the gas flux.
Metals such as zirconium (Zr), titanium (Ti), tantalum (Ta) and yttrium (Y) used in the getters are capable of dissolving their own chemically formed oxides, nitrides and carbides in the solid-state form at elevated temperatures. For example, Zr has a better gettering capability compared to Ti since the gettering effect of pure Ti is very low due to oxidation and other contamination. As a result, commercial getters are primarily Zr-based alloys which can seclude a vacuum level of about 1 mTorr. Nevertheless, Zr powders have high activity and are easily flammable and explosive.
Therefore, there remains a need to provide for alternative getter technology for use MEMS devices to overcome the above problem.